7 - Medium - 两数相加

给定两个非空链表来表示两个非负整数。位数按照逆序方式存储，它们的每个节点只存储单个数字。将两数相加返回一个新的链表。

你可以假设除了数字 0 之外，这两个数字都不会以零开头。

示例：

输入：(2 -> 4 -> 3) + (5 -> 6 -> 4)
输出：7 -> 0 -> 8
原因：342 + 465 = 807

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution(object):
    def addTwoNumbers(self, l1, l2):
        """
        :type l1: ListNode
        :type l2: ListNode
        :rtype: ListNode
        """
        n1, n2 = 0, 0
        mul = 1
        while l1:
            n1 += l1.val * mul
            mul *= 10
            l1 = l1.next
        mul = 1
        while l2:
            n2 += l2.val * mul
            mul *= 10
            l2 = l2.next
        n = n1 + n2
        dummy = ListNode(0)
        p = dummy
        while n >= 10:
            temp = n % 10
            n = (n - temp) // 10
            p.next = ListNode(temp)
            p = p.next
        p.next = ListNode(n)
        return dummy.next

只循环一次

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution(object):
    def addTwoNumbers(self, l1, l2):
        """
        :type l1: ListNode
        :type l2: ListNode
        :rtype: ListNode
        """
        if l1 is None:
            return l2
        if l2 is None:
            return l1

        tmp = ListNode(0)
        res = tmp
        flag = 0
        while l1 or l2:
            tmpsum = 0
            if l1:
                tmpsum = l1.val
                l1 = l1.next
            if l2:
                tmpsum += l2.val
                l2 = l2.next
            tmpres = ((tmpsum + flag) % 10)
            flag = ((tmpsum + flag) // 10)
            res.next = ListNode(tmpres)
            res = res.next
        if flag:
            res.next = ListNode(1)
        res = tmp.next
        del tmp
        return res

不要虚头结点

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution:
    def addTwoNumbers(self, l1, l2):
        """
        :type l1: ListNode
        :type l2: ListNode
        :rtype: ListNode
        """
        if l1 is None:
            return l2
        if l2 is None:
            return l1
        head = ListNode(0)
        res = head
        profit = 0
        while l1 or l2:
            _sum = 0
            if l1:
                _sum += l1.val
                l1 = l1.next
            if l2:
                _sum += l2.val
                l2 = l2.next
            _val = (_sum + profit) % 10
            profit = (_sum + profit) // 10
            res.val = _val
            if l1 or l2:
                res.next = ListNode(0)
                res = res.next
        if profit:
            res.next = ListNode(1)
        return head